To develop and use an animal model for studying immune responses to antigen expressed in healthy and neoplastic intestine, addressing: 1) The role of thymus in tolerance of gut specific antigens and the generation of regulatory T cells (Treg), 2) The role of encounter of antigen in the periphery on the maturation and survival of Treg, 3) The immunologic consequences of delayed as compared with constitutive gut specific expression of antigen, 4) The influence of tumor growth on immune responses and tolerance.